This invention relates to managing payload specific latencies in a cross-connect system.
In a synchronous transmission system or network, data traffic takes the form of synchronous data signals comprised of data frames. Data traffic is transported in high order or low order data structures, where a high order structure may include more than one low order structure. For example, a synchronous digital hierarchy (SDH) system carries data in structures known as virtual containers (VCs), which may be high order containers, for example a VC-4, or low order containers, for example a VC-11 or VC-12. For example, a VC-4 may include 63 VC-12s or two low order VC-3s and 21 VC-12s. The VCs are transported across a network in frames known as synchronous transport module (STM) frames. Similarly, a synchronous optical network (SONET) system carries data in high order structures known as synchronous transport signals (STS) or low order structures known as virtual tributaries (VTs). An STS-1 may include some combination of lower signals such as 28 VT1.5s or 21 VT2s, where VT2s are comparable with SDH VC-12s. VC-11s and VC-12s are transported in tributary units TU-11 and TU-12 respectively.
In some cases, is not desirable for network equipment to provide full low order switching. It is, however, desirable for network equipment to provide some low order switching of VT (VT1.5/VT2) and/or TU (TU11/TU12) rate signals. This is commonly known as partial VT/TU switching. A system including both a VT/TU switching apparatus and an STS switching apparatus provides partial VT/TU switching. In such an arrangement, the high-order (STS/VC-3/VC-4) switch passes to the VT/TU switch only VT/TU traffic that requires switching (where switching normally includes timeslot interchanging and/or port interchanging).